The extreme genetic diversity of HIV-1 isolates poses a major challenge for the development of an HIV vaccine. Recent studies in mice have suggested that using "centralized" HIV-1 sequences in immunogens may be an effective strategy for minimizing the impact of this genetic diversity on the creation of effective vaccines. Simian immunodeficiency virus (SIV) and the simian human immunodeficiency virus (SHIV) infected rhesus monkeys provide a powerful model for evaluating potential HIV vaccine strategies. We will employ this animal model to explore the use of "centralized" gene-based HIV-1 vaccine strategies for broadening the recognition specificity of vaccine-elicited immune responses. Specifically, we will use this model to explore the: 1. Selection of an optimal "centralized" HIV-1 envelope immunogen. 2. Comparison of "centralized" and contemporary HIV-1 gag-pol-nef immunogens. 3. Comparison of "centralized" and multiclade HIV-1 immunogens 4. Assessment of recombinant MVA "centralized" HIV-1 immunogens. 5. Evaluation of "centralized" envelope subunit immunogens.